PubMed Health⌕ Search

Biomedical subjects

H Pritzkow

Publications and source records attributed to H Pritzkow.

9 recordsLinked to original sources
PubMed2001

Template synthesis of a tetraazamacrocyclic ligand with two pendant pyridinyl groups: properties of the isomers of the metal-free ligand and of their first-row transition metal compounds.

The one-step reaction of [Cu(en)(2)](2+) (en = 1,2-diaminoethane) with formaldehyde, ethyl 2-pyridyl acetate, and base produces a mixture of [Cu(s-pypymac)](2+) and [Cu(a-pypymac)](2+) (s-pypymac = syn-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane, a-pypymac = anti-6,13-bis(2-pyridinyl)-1,4,8,11-tetraazacyclotetradecane; syn-to-anti ratio approximately 1:9) in low yield (6%). Ion exchange chromatography is used for isomer separation, and the two isomers of the metal-free ligand are obtained by reduction of the copper(II) complexes and subsequent ion exchange chromatography. Crystal structure analyses of the metal-free a-pypymac ligand, of two isomeric copper(II) compounds of a-pypymac and one of s-pypymac, and of the cobalt(III) complexes of a- and s-pypymac and nickel(II), as well as zinc(II) complexes of a-pypymac, are reported and discussed on the basis of the expectations from force field calculations and from published experimental data of the transition metal compounds of the bis-pendant amine derivative diammac.

Journal Article↗
PubMed2001

An allosteric synthetic catalyst: metal ions tune the activity of an artificial phosphodiesterase.

A trinuclear metal complex of general formula (L-H)M3(Mf)2 represents the first allosteric low molecular weight catalyst. L is a polyaza ligand having a tetradentate and two bidentate metal binding sites, Ms is a "structural" (allosteric) metal, and Mf are functional (catalytic) metals which interact with a substrate. In mononuclear [(L-H)Ms]+ complexes [(L-H)Cu(MeOH)]ClO4 (1a). [(L-H)Cu]NO3 x 2H2O (1b), [(L-H)Ni]ClO4 x 4H2O (2), and [(L-H)Pd]ClO4 x 2H2O (3), prepared from L and M2+ salts, the metal is strongly bound by an in-plane N4-coordination (confirmed by X-ray crystal structure determination of la). Formation of trinuclear complexes [(L-H)MsCu2]5+, with two functional Cu2+ ions coordinated to the bidentate sites of L, was evidenced in solution by photometric titration and by isolation of [(L-H)Cu3][PO4][ClO4]2 x 9H2O (4). The trinuclear complexes catalyze the cleavage of RNA-analogue 2-(hydroxypropyl)-p-nitrophenyl phosphate (HPNP), an activated phosphodiester. From a kinetic analysis of the cleavage rate at various HPNP concentrations, parameters KHPNP (the equilibrium constant for binding of HPNP to [(L-H)MsCu2]5+ and kcat (first-order rate constant for cleavage of HPNP when bound to the catalyst) were derived: KM= 170 (Ms= Cu2+), 340 (Ms = Ni2+), 2,600 (Ms = Pd2+) M(-1), kcat = 17 x 10(-3) (Ms= Cu2+) 3.1 x 10(-3) (Ms=Ni2+), 0.22 x 10(-3) (Ms = Pd2+) s(-1). Obviously, the nature of the allosteric metal ion Ms strongly influences both substrate affinity and reactivity of the catalyst [(L-H)MsCu2]5+. Our interpretation of this observation is that subtle differences in the ionic radius of Ms and in its tendency to distort the N4-Ms coordination plane have a significant influence on the conformation of the catalyst (i.e., preorganization of functional Cu2+ ions) and thus on catalytic activity.

Allosteric Regulation↗
PubMed2001

Poly[[[1,2-mu)-benzene]silver(I)-mu-trifluoromethanesulfonate-O;O';O":O"].

The title compound, [Ag(CF(3)O(3)S)(C(6)H(6))], has been synthesized and characterized by low-temperature single-crystal X-ray diffraction. The complex is polymeric, with a network of trifluoromethanesulfonate anions bridging the silver cations. The terminal planar benzene ligand is asymmetrically eta(2)-coordinated to the Ag.

Journal Article↗
PubMed2000

A copper(I) oxygenation precursor in the entatic state: two isomers of a copper(I) compound of a rigid tetradentate ligand

Oxygenation of [CuI(L1)(NC-CH3)]+ (L1 = dimethyl 2,4-bis(2-pyridinyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate) leads to a relatively stable mu-peroxo-dicopper(II) product. The stability of this type of oxygenation product has been shown before to be the result of the square pyramidal geometry of L1; preorganization by a dinucleating ligand has been shown to increase the stability of the mu-peroxo-dicopper(II) compound. The structural data presented here indicate that destabilization of the copper(I) precursor is another important factor. There are two isomers of [CuI(L1)(NCCH3)]+; one is yellow, and the other is red. X-ray crystallography indicates that one pyridinyl donor is not coordinated in the yellow compound and that the red compound is 5-coordinate. In the light of the X-ray structure of the metal-free ligand and that of the corresponding copper(II) compound, it emerges that the ligand cavity is well suited for copper(II), whereas the copper(I) compounds are highly strained. This is supported by 1H NMR spectra of the copper(I) species where a fast dynamic process leads to line broadening and by electrochemical data, which indicate that the copper(II) products are exceptionally stable. Also presented are structural (copper(II)), electrochemical, and spectroscopic data (1H NMR, copper(I)) of the derivative [Cu(L2)(X)]n+ with a methyl substituent at the alpha-carbon atom of the two coordinated pyridinyl groups (L2 = dimethyl 2,4-bis(2-pyridinyl-6-methyl)-3,7-diazabicyclo-[3.3.1]-nonane-9-on-1,5-dicarboxylate). There are two structural forms of [CuII(L2)(X)]n+ (X = NCCH3, Cl), which depend on the steric demand of the fifth donor X. For both, van der Waals repulsion leads to a destabilization of the copper(II) products, and this is also evident from an increase in the reduction potential (-110 mV vs. -477 mV, Ag/AgNO3).

Journal Article↗
PubMed2000

Macrocyclic Imidazolylboranes.

Cycles, not chains: 1-imidazolylboranes exist in polymeric form as a consequence of donor/acceptor interactions. Through the use of suitable substituents and under high dilution tetrameric and pentameric macrocyclic imidazolylboranes were synthesized. The picture shows the structure of the tetrameric 4,5-dimethylimidazolylborane (black: C, gray: B, white: N).

Journal Article↗
PubMed1999

Lithiated Clusters from Primary Silylphosphanes and Silylarsanes: Spherical Bodies with and without Li(2)O Filling.

Molecular clusters with archimedean and platonic shape, which in order to build a closed polyhedron, spontaneously eliminate H(2) or voluntarily encapsulate Li(2)O as a "cluster nucleus", result from the dilithiation of primary silylphosphanes and silylarsanes with BuLi. Thus, the first mixed-valent, decameric P(10)Li(16) cluster 1 was obtained from iPr(3)SiPH(2) and tBuLi (molar ratio 1:2) with strict exclusion of LiOH and Li(2)O, whereas partial metalation in the presence of LiOH initially leads to a dodecameric, Li(2)O-containing cluster 2, from which the three-shell cluster 3 with a [Li(6)O](4+) core is obtained.

Journal Article↗